“I have zero level of concern at this stage,” James said. “I didn’t go to college, so it’s not March Madness. You know, you get better throughout the series. You see ways you can get better throughout the series. But I’ve been down 0-1, I’ve been down 0-2. I’ve been down before in the postseason. But for me, there’s never a level of concern no matter how bad I played tonight, with seven turnovers, how inefficient I was shooting the ball. I’m just as confident going into a series whether it’s a 0-0 series or I’m down 0-1.”

Well, OK then.

Not much went right for LeBron James and Kevin Love on Sunday in Game 1. (AP)

James has earned the benefit of the doubt, right? Want adversity? Travel all the way back to Game 2 of the conference quarterfinals, against Indiana. Cleveland had lost Game 1 — at home, no less — and the pesky Pacers were threatening to take a 2-0 series lead. LeBron’s response? Putting up 46 points on 71 percent shooting in a three-point win.

“Game 1 has always been a feel-out game for me,” James said.

Still, Boston isn’t Indiana, and a 2-0 hole against the Celtics is damn near insurmountable, given the way Boston’s Improbable Team has been playing. “Totally different team, different series,” J.R. Smith said. On Saturday, Marcus Morris declared himself to be the best ’Bron defender this side of Kawhi Leonard. On Sunday, he backed it up, limiting James to 15 points, while chipping in 21 points and 10 rebounds.

“I’m a competitor,” Morris said. “He’s the best player. I’m going to be able to tell my kids this one day. It’s exciting. I love the challenge. But it’s a team effort.”

Morris nearly wasn’t as big a part of it. A few minutes into the first quarter, Morris picked up his second foul. Many coaches would have pulled him. Brad Stevens didn’t. As a player, Stevens remembered his rhythm breaking when he was yanked with foul trouble. So, he says, “Ninety-nine percent of the time I lean on the side of not taking [a player] out.” He left Morris in — and Morris picked up just one more foul the rest of the way.

“If he fouls out in the first quarter, somebody else has to play,” Stevens said. “That’s the way it goes.”

James said he will review the game film Monday, and there is a lot for him to dive into. “[Boston] showed [James] two bodies all night,” Cavs coach Tyronn Lue said. “When they thought he had driving lanes, they helped, making him kick it out to our shooters.” Those shooters missed, 14 straight times from 3-point range, to be exact. The Cavs made just 36 percent of their shots, were outrebounded (48-40) and surrendered 60 points in the paint.

Not that James is worried. As he walked down a hallway, he passed photos of great moments in Celtics history on the concrete walls. James has been a casualty of some of them — his Cavs were dispatched by the Celtics in Boston’s 2008 title-winning postseason run — but he has prevented a few more of those moments, too. In 2011, his Miami Heat dispatched Boston in five games; in ’12, the Heat rallied from a 3-2 deficit in the conference finals, effectively ending the Celtics’ “Big Three” era.

“Every year is a different challenge, no matter if you are going up against the previous Celtics team or the present,” James said.

On Tuesday, James will have a new one. Boston is bracing for a superior performance — “We’ll get a heavyweight punch on Tuesday night,” Stevens said — and is scheming accordingly. The Celtics see making James defend as a big part of slowing him down, so they won’t holster Morris and will encourage Jayson Tatum, Jaylen Brown, Terry Rozier and Marcus Smart to attack when James is guarding them. Stevens admits that Boston struggled to play with poise against Cleveland last season. This year, this team might not.

“We have a lot of guys that really just don’t care,” Smart said. “Our whole life we’ve been fighting bigger opponents than us. And playing LeBron and that Cavs team is great. They’ve been here for a reason. We have talent as well. We’re fearless.”

A young team, a fierce opponent, a building that holds memories for James, good and bad. James doesn’t dismiss Boston’s efforts; he’s just quick to remind everyone when they did it. Morris’ defense was solid … in Game 1, James said. Stevens’ game plan was sound … in Game 1, James made sure to add. His message: It has been 15 years and 229 playoff games. He won’t get lost in one.

“I’ve got a good sense of the way they played me today, and how I’ll play going into Game 2,” James said. “We have another opportunity to be better as a ball club coming Tuesday night, and we’ll see what happens.”